Bukkit

Worldgenerator for a scandinavian/nordic look

A pretty easy-to-use in-game biome editor (requires WorldEdit to work)

Save, load, reset any worlds.

The Hidden Lorax will automatically plant saplings left on the ground.

The Best Plugin for Integrating Adventure Maps onto your Server

Permanent world generator.

A plugin that randomly will generate .schematic files into your world.

Mineral Vein

World Regeneration, Factions Wilderness Regeneration

Removes all ores that can only be found by branch-mining while retaining all ores that can be found by caving and exploring

RandomEncounters adds configurable random structure, treasure, and mob generation to the world

Explore a randomly generated Dungeon packed with loot

emericaWorlds is a World Generator and a Teleporter

A simple void world generator.

Cobblestone Generators will create ores as well as cobblestone

WorldCreator

Creates a slightly less boring flat world for creative

Libelula Ultimate Capture The Wool

world generator based on sethbling's MCEdit filter

OreRate